Basic System Problem Analysis - August 2003

Dispatcher Structures

These are not the only dispatcher structures but they are worth mentioning in this context.

The TCB, or task control block rates a special mention because it is the structure use to

save process state when a process looses the CPU.

It is kept in real memory but is “equivalently mapped” meaning that it is given an address

in space 0 at the same offset it occupies in real memory.

The TCB function will return the real memory address of a TCB for a given PIN. You

cannot format real memory using the FV command. Since the TCB is equivalently

mapped into space 0 you can supply that creating a virtual address from the real address

returned by the TCB function, for example:

$217 ($70) nmdat > wl TCB(pin)

$8c01d00

$218 ($70) nmdat > fv 0.TCB(pin) 'TCB_TYPE'

RECORD

STACK_BASE : 41854000

STACK_LIMIT : 418b4000

STK_ADDR_NOT_IN_CACHE : 418aa000

Another useful thing to note about the TCB is that since it stores state information about a

process it can use used in a dump to restore that state. That is, you can try to rewind a

process to the state it was in the last time it lost the CPU. For example:

$219 ($70) nmdat > tr,d,i

PC=a.0019fe78 system_abort

NM* 0) SP=418562e0 RP=a.00a51bc8 sm_quarantine_gufd+$1fc

NM 1) SP=418562e0 RP=a.00ee5a5c

tm_close_common.tm_unlink_plfd_and_gdpd+$184

NM 2) SP=418558e0 RP=a.00ee75cc tm_close_common+$1a98

NM 3) SP=41855860 RP=a.0158a8e4 tm_ord_fix_buf_disc+$1e4

NM 5) SP=418547e0 RP=a.01163d68 ?fclose_nm+$8

$21a ($70) nmdat > initnm tcb

$21b ($70) nmdat > tr,d,i

PC=a.00394f78 $$lr_wa_14_long

NM* 0) SP=418565a0 RP=a.010722c0 sd_log_data+$504

NM 1) SP=418565a0 RP=a.01072ca8 sdump_data+$108

NM 2) SP=418564a0 RP=a.009d6140 sdump_dump_navigation_structure+$328c

NM 3) SP=418563e0 RP=a.00a51b98 sm_quarantine_gufd+$1cc